docs: def timespan(self, from_date, to_date=None, span=None, current=False):
          """
          Takes a beginning date a filters entries. An optional to_date can be
          specified, or a span, which is one of ('month', 'week', 'day').
          N.B. - If given a to_date, it does not include that date, only before.
          """
          if span and not to_date:
              diff = None
              if span == 'month':
                  diff = relativedelta(months=1)
              elif span == 'week':
                  diff = relativedelta(days=7)
              elif span == 'day':
                  diff = relativedelta(days=1)
              if diff is not None:
                  to_date = from_date + diff
          datesQ = Q(end_time__gte=from_date)
          datesQ &= Q(end_time__lt=to_date) if to_date else Q()
          datesQ |= Q(end_time__isnull=True) if current else Q()
          return self.filter(datesQ)